Chap. 10.] Mate. 55 



contains. Stone-marie differs from clay-marie only 

 in being much harder ; but it differs from ordinary 

 ftone by breaking to pieces when expofed to the air. 



It has been fuppofed by fome refpectable writers, 

 that all thefe fpecies of calcareous earth derive their 

 origin from iheJls. Some marbles are evidently 

 formed of fhells, and thofe of Derbyfhire exhibit this 

 appearance in a remarkable manner. Coral is univer- 

 fally allowed to be the work of fmall animals of the 

 polypus kind. The ftrata of limeftone being alfo 

 found fo frequently united with (hells and other marine 

 fubftances, has induced the philofophers to whom I 

 allude to believe, that the ftdne itfelf is altogether com- 

 pofed of ihells, which at firft mouldered into pafte, and 

 were afterwards preffed and concreted together. In 

 one of the quarries of Italy, the bones of fmall fifties 

 are found j and fome rocks in the midland counties of 

 England are almoft wholly cornpofed of the kind of 

 fhells called entrocbi. The animals which produce 

 the coral are here feldom to be found ; but in other 

 parts, as in Jamaica, the bottom of the fea is entirely 

 covered over with coral, and harbours are fometimes 

 flopped up with it. Sir Hans Slcane mentions a 

 Spanifh plate-fhip, which was wrecked, and remained 

 at ihe bottom of the fea twenty-five years, being then 

 fifhed for, the treafure, as well as the timber, &c. 

 were covered, with coraline concretions. Hence, this 

 tonftant growth at the bottom of the fea may in time 

 produce beds and ftrata of this kind of earth, which, 

 according to circumftances, may be converted ',n:o 

 marie, limeftone, marble, &c. Calcareous earths, 

 united with carbonic acid, may be known under all 

 forms, by effervefcence with the mineral acids. 



6. If vitriolic acid is poured on chalk, the carbonic 



acid is expelled, while the vitriolic unices with the 



E 4 calcareous 



